Engine controller and engine control method

Abstract

An engine controller includes an ignition timing control unit and a rich imbalance determining unit. The rich imbalance determining unit designates one of multiple cylinders as a subject cylinder for determination and executes lean active control that commands a smaller amount of fuel injection for the subject cylinder than for the other cylinders. The rich imbalance determining unit determines whether an air-fuel ratio of the subject cylinder deviates to be richer based on a rotational fluctuation amount of a crankshaft during the execution of the lean active control. The ignition timing control unit executes an advancement limiting process that limits advancement of the ignition timing by the knock control during the execution of the lean active control.

What is claimed is: 
     
       1. An engine controller configured to control an engine that includes cylinders, the engine controller comprising:
 an ignition timing control unit that controls ignition timing of the engine, the ignition timing control unit being configured to execute knock control that advances the ignition timing while knocking is not detected and retards the ignition timing when knocking is detected, thereby adjusting the ignition timing to a trace knock point that is an advancement limit of the ignition timing at which knocking can be suppressed; and 
 a rich imbalance determining unit that designates one of the cylinders as a subject cylinder for determination, the rich imbalance determining unit being configured to execute lean active control that commands a smaller amount of fuel injection for the subject cylinder than for the other cylinders, and to determine whether an air-fuel ratio of the subject cylinder deviates to be richer based on a rotational fluctuation amount of a crankshaft during the execution of the lean active control, 
 wherein the ignition timing control unit is configured to execute an advancement limiting process that limits advancement of the ignition timing by the knock control during the execution of the lean active control. 
 
     
     
       2. The engine controller according to  claim 1 , wherein the ignition timing control unit is configured to execute, even when the advancement limiting process is being executed, retardation of the ignition timing in the knock control in a same manner as in a state in which the advancement limiting process is not being executed. 
     
     
       3. The engine controller according to  claim 1 , wherein the ignition timing control unit is configured to
 execute the knock control by updating a value of a knock control amount, which is an advancement correction amount of the ignition timing for the knock control, in accordance with whether knocking has been detected, and 
 execute the advancement limiting process by limiting an update range of the value of the knock control amount up to an upper limit guard value. 
 
     
     
       4. The engine controller according to  claim 1 , wherein the ignition timing control unit is configured to
 learn an adjustment amount of the ignition timing by the knock control as a knock learning value, and 
 suspend the learning of the knock learning value during the execution of the advancement limiting process. 
 
     
     
       5. An engine control method of controlling an engine that includes cylinders, the engine control method comprising:
 executing knock control that advances ignition timing while knocking is not detected and retards the ignition timing when knocking is detected, thereby adjusting the ignition timing to a trace knock point that is an advancement limit of the ignition timing at which knocking can be suppressed; 
 designating one of the cylinders as a subject cylinder for determination; 
 executing lean active control that commands a smaller amount of fuel injection for the subject cylinder than for the other cylinders; 
 determining whether an air-fuel ratio of the subject cylinder deviates to be richer based on a rotational fluctuation amount of a crankshaft during the execution of the lean active control; and 
 limiting advancement of the ignition timing by the knock control during the execution of the lean active control. 
 
     
     
       6. An engine controller configured to control an engine that includes cylinders, the engine controller comprising a processing circuit that is configured to:
 execute knock control to control ignition timing of the engine, wherein the knock control advances the ignition timing while knocking is not detected and retards the ignition timing when knocking is detected, thereby adjusting the ignition timing to a trace knock point that is an advancement limit of the ignition timing at which knocking can be suppressed; 
 designate one of the cylinders as a subject cylinder for determination; 
 execute lean active control that commands a smaller amount of fuel injection for the subject cylinder than for the other cylinders; 
 determine whether an air-fuel ratio of the subject cylinder deviates to be richer based on a rotational fluctuation amount of a crankshaft during the execution of the lean active control; and 
 execute an advancement limiting process that limits advancement of the ignition timing by the knock control during the execution of the lean active control.